The present invention relates to the field of boring and excavating screens in ground. A particular application is to be found in the context of making works that are very deep, in particular having a depth of more than about fifty meters.
The term “screen” is used particularly, but not exclusively, to mean diaphragm walls that are molded in the ground.
More particularly, the invention relates to a method of making a continuous wall in ground, the method comprising the following steps:                providing an excavation machine having a frame with a longitudinal direction, said frame having a bottom end and carrying a cutter device arranged at its bottom end;        performing a step of making a first screen in the ground, which step includes a first boring step using the excavation machine; and        performing a second boring step using the excavation machine in order to make a second screen in the ground that is juxtaposed with the first screen in such a manner that the first and second screens are secant.        
The excavation machine used in the method is generally a rotary drum borer, as described in FR 2 211 027. The machine is suspended from a hoist by cables.
During the first boring step, the frame moves downwards as its cutter device digs the trench.
For certain works, the trench may present great depth, which may extend to one hundred meters or more.
In addition, it is generally necessary for the trench to be very accurate in terms of its verticality, in particular since the final wall is the result of juxtaposing secant screens.
Nevertheless, because of the presence of irregularities in the ground, there are major risks of the frame departing from its vertical path, with this risk being even greater for works of great depth.
There is thus a major risk of the final wall not being continuous, or of being secant only over an overlap thickness that is not sufficient.
Insofar as the final wall usually needs to be waterproof, it can be understood that there exists a real need to be able to ensure that the wall that is made is indeed continuous.
In order to solve this problem, in particular in the context of boring to great depths, it is known to increase the thickness of the screen. Nevertheless, that solution leads to a significant increase in the resources that are consumed and in the cost of making the continuous wall, and that is not desirable.